1. Field of the Invention
The present invention relates to the technical field of two-dimensional optical identification and, more particularly, to a two-dimensional optical identification device with same gray level.
2. Description of Related Art
For increasing the convenience, fun, and efficiency of reading a document, a typical way embeds optical identification codes into pictures in which the optical identification codes are printed on the document. An external reader can thus read the optical identification code corresponding to a part of pictures, and activate an output device to, for example, play a voice based on the read optical identification code. Thus, the played voice can effectively help the reading. However, such a technique has to embed the optical identification code into the pictures of the document, which certainly causes the complexity of making a document and affects the picture display. Therefore, it is desired to accurately read the optical identification code without being affected by the pictures.
In the known patents, U.S. Pat. No. 7,530,496 granted to Chen for a “Surface sensitive input device with indexes and computer system using the input device” discloses a layer of points corresponding to an optical identification code added onto a raw image, as show in FIG. 1. The optical identification code 100 of FIG. 1 has a plurality of indexing points in an isotropic arrangement. The indexing points are tiny and thus invisible to human eyes. As shown in FIG. 1, such indexing points are arranged in an isotropic manner, each indexing point having a radius of about 100 μm. The indexing points include a center point 110, a plurality of direction points 121 and 122, a plurality of first data points 131-136, and a plurality of second data points 1401-1412. The direction point 122 is provided as a direction recognition point in blank or hollow, in which the hollow direction point 122 is used to represent no point printed.
Such an optical identification code 100 can present a different picture object capable of being read by an optical reader for further processing. For example, different optical identification codes representing different picture objects correspond to different voices, respectively, and accordingly a corresponding voice can be played when the optical reader reads a picture object.
However, as shown in the optical identification code 100 of FIG. 1, the locations of the first data points 131-136 and the second data points 1401-1412 at the outer circle are determined by using the center point 110, a direction point 121 and five direction points 122. Since there is no auxiliary positioning point on the outer circle, it is possible to have a deformed picture taken by a slant lens, which further increases the difficulty of locating the data points. Also, since a blank indicates no printed point, it is likely to have an effect of non-uniform gray level when multiple optical identification codes 100 are printed in a picture object. Further, when the same information is carried, the patterns of the optical identification codes 100 are the same, resulting in the generation of texture feeling on vision.
FIG. 2 schematically illustrates another optical identification code 200. The optical identification code 200 is comprised of one positioning block 201 and eight coded data blocks 202-209 arranged in a nine-square grid. Each center of the coded data blocks 202-209 is filled up and used as an auxiliary positioning point to thereby avoid the difficulty on locating the data points due to lack of auxiliary positioning point on the outer. The positioning block 201 has five points filled up and used as major positioning points to reduce the difficulty of locating the data points. However, the major positioning points of the block 201 are obvious to see, in which users can easily sense a texture when the optical identification codes 200 repeatedly present on the surface of a picture. In addition, the auxiliary positioning points and data points contained in the coded data blocks 202-209 can cause a non-uniform distribution of the data points, resulting in producing the effect of non-uniform gray level.
FIG. 3 schematically illustrates a further optical identification code 300. The optical identification code 300 is comprised of a content part 310 and a position part 320. The content part 310 has nine coded data blocks, and the position part 320 has seven positioning blocks. The position part 320 is arranged at two adjacent sides of the content part 310. In this case, in order to improve the equality effect of gray level, all positioning points are arranged at the outer with a shifted point 321 to indicate the direction information. However, for the same gray level, all data points 311 are placed in proximity to an intersection of virtual lines 313 and 315, with a small offset. In addition, since all positioning points arranged at the outer part are obvious, it is likely to produce a texture feeling on vision when the optical identification code 300 is repeatedly present.
Therefore, it is desirable to provide an improved optical identification device to mitigate and/or obviate the aforementioned problems.